1. Field of the Invention
The present invention relates to a plasma display panel. More particularly, the present invention relates to an apparatus and method for driving a plasma display panel to enhance the display of gray scale and color.
2. Description of the Related Art
A plasma display panel (PDP) is a display device in which a plurality of discharge cells are arranged in a matrix, and the discharge cells are selectively illuminated to restore image data, which are input as electrical signals.
In such a PDP, a plurality of scan electrodes and sustain electrodes are formed with at least one pair opposing one another in parallel, and at least one address electrode is formed at a predetermined distance from these electrodes and orthogonal to the same. A pulse voltage is applied to at least one of the scan electrodes and the sustain electrodes, and an address voltage is applied to the address electrode. As a result, discharge occurs between the address electrodes and the scan electrodes and/or the sustain electrodes to thereby realize an address operation that provides variations in electrical properties where these electrodes intersect. Also, a sustain operation is performed in which a sustain voltage is applied between the scan electrodes and the sustain electrodes following discharge such that discharge occurs only at locations where variations in electrical properties arise between the scan electrodes and the sustain electrodes.
In such a PDP, the display of gray scale must be possible in order to exhibit the capabilities of a color display device. A method is used to achieve this, in which a single field is divided into a plurality of sub-fields and the sub-fields are controlled by a process of time sharing.
The drive characteristics of PDPs are such that a high amount of power is consumed during operation. Therefore, an automatic power control (APC) technique is used in which the amount of power consumed is controlled according to a load ratio (or an ASL (average signal level)) of a displayed frame. That is, in the APC technique, the power consumed is limited to below a predetermined level while the number of sustain pulses is varied according to the load ratio of input image data.
With the use of the APC technique, the number of sustain pulses operating on each sub-field is varied according to the load ratio. In particular, depending on the load ratio, the number of total sustain pulses applied in 1 TV frame is varied such that each sub-field has a number of sustain pulses corresponding to a gray scale display weight that the sub-field has. Therefore, the number of sustain pulses operating on each sub-field also varies.
In the ideal case, in order to realize a linear relation between gray scale and the number of sustain pulses, the number of sustain pulses must be a real number. However, in practice, the number of sustain pulses must be an integer to realize such an outcome, in which case a quantization error results during generation of the number of sustain pulses.
For example, a number nij of sustain pulses of a jth APC level of an actual ith sub-field is obtained as shown in Equation 1 below.
                              n                      i            ⁢                                                  ⁢            j                          =                                            w              i                                                      ∑                                  i                  =                  1                                                  N                                      s                    ⁢                                                                                  ⁢                    f                                                              ⁢                                                          ⁢                              w                i                                              ⁢                      N            TOTj                                              [                  Equation          ⁢                                          ⁢          1                ]            
where Wi is a gray scale display weight of an ith sub-field, Nsf is a number of sub-fields, and NTOTj is a total number of sustain pulses of a jth APC level.
The number nij of sustain pulses calculated using Equation 1 above is either an integer or a real number, whereas the number of sustain pulses used in practice is an integer. Therefore, during actual PDP driving, the number nij is rounded to the nearest whole number to obtain the number Nij. The quantization error resulting from such rounding is expressed as δNij. The corresponding relation is shown in Equation 2 below.Nij=Round(nij)nij=Nij+δNij  [Equation 2]
Accordingly, with respect to the jth APC level, a designated total number of sustain pulses and a total number of sustain pulses actually obtained are not the same, and a difference between these amounts may be expressed as a sum of the quantization errors as shown in Equation 3 as follows.
                                          N            TOTj                    -                                    ∑                              i                =                1                                            N                                  s                  ⁢                                                                          ⁢                  f                                                      ⁢                                                  ⁢                          N                              i                ⁢                                                                  ⁢                j                                                    =                                            ∑                              i                =                1                                            N                                  s                  ⁢                                                                          ⁢                  f                                                      ⁢                          δ              ⁢                                                          ⁢                              N                                  i                  ⁢                                                                          ⁢                  j                                                              ≠          0                                    [                  Equation          ⁢                                          ⁢          3                ]            
Quantization error rates with respect to each APC level are shown in FIG. 1. It is clear from the drawing that the larger the load ratio of the screen, the greater the spread in the quantization error rate during load ratio variations.
The gray scale display weights of the sub-fields for the different load rates become slightly distorted by the quantization errors. This causes a reduction in the ability to display gray scale such that gray scale colors are distorted according to load ratio variations. As shown in FIGS. 2A and 2B, compared to before quantization, colors are distorted following quantization when the APC levels are converted at the same gray levels when displaying low gray levels.
While driving the PDP, if gamma correction is performed, which is reverse correction of gray scale correction with respect to digital image data, gray scale in the displayed image that is low in brightness is significantly lowered to thereby deteriorate picture quality. To remedy this problem, Korean Laid-Open Patent No. 2002-14766 discloses a technique in which error components of gray scale displayed following an increase in gray scale during gamma correction are diffused to adjacent pixels. As an example, in the case where image data input for gamma correction are 8 bits, data output through gamma correction are converted to data of 12 bits. Subsequently, the lower 4 bits of the 12 bits are separated by error diffusion and diffused to an adjacent pixel such that ultimately 8-bit data able to display low gray scale are input to the PDP.
However, in such a conventional method, compensation with respect to quantization errors occurring when the APC technique is applied as described above is not performed, and the errors caused by the inaccuracy in the number of sustain pulses are diffused to an adjacent pixel. As a result, a rate at which the consumed power varies according to the load ratio lacks uniformity.